/Engine/Source/Runtime/RHI/Public/RHIContext.h
Performs a copy of the data in 'SourceBuffer' to 'DestinationStagingBuffer.' This will occur inline on the GPU timeline. This is a mechanism to perform nonblocking readback of a buffer at a point in time.
virtual void RHICopyToStagingBuffer ( [FRHIBuffer](API\Runtime\RHI\FRHIBuffer) * SourceBufferRHI, [FRHIStagingBuffer](API\Runtime\RHI\FRHIStagingBuffer) * DestinationStagingBufferRHI, uint32 InOffset, uint32 InNumBytes )